Add sneak and sneak_glitch to set_physics_override()

doc/lua_api.txt

src/content_cao.cpp

src/content_sao.cpp

src/content_sao.h

src/genericobject.cpp

src/genericobject.h

src/localplayer.cpp

src/player.cpp

src/player.h

src/script/lua_api/l_object.cpp

src/script/lua_api/l_object.h